Gilead Sciences Inc. (GILD), the world’s largest maker of HIV drugs, has spent $1.2 billion in two years to buy blood cancer drugs. It’s looking for more. Treatment for leukemia and other blood cancers is one of the fastest growing markets for cancer drugs. Gilead’s recent string of four deals is intended to tap into that market and set the stage for the company’s growth for years. In the last year, 11 of 39 new drug therapies approved in the U.S. involved stopping cancers by targeting their underlying genetic structure. As of October 2012, investors were focused on at least 14 medicines in final testing for blood malignancies with the potential to move stocks, according to a report by Cowen & Co. analyst. Gilead Chief Operating Officer John Milligan said the company is eying deals in this universe. “Oncology is entering an era where significant advances are going to be made, far above and beyond what’s been made previously,” Milligan said. “It’s a field where there’s always the possibility of acquiring other molecules and companies as their technology or pipelines mature. We’re certainly keeping our eye on it.” While Milligan wouldn’t discuss possible acquisitions for his Foster City, California-based company, they may include two biotechnology companies based in Cambridge, Massachusetts, Ariad Pharmaceuticals Inc. (ARIA) and Infinity (INFI) Pharmaceuticals Inc., said Raghuram Selvaraju, at Aegis Capital Corp. “There is a massive amount of untapped potential in the hematological malignancy space,” said Selvaraju, who is head of health-care equity research at the New York-based company.